The present invention relates to a primary air and fuel supply for a combustion chamber of a gas turbine engine.
In the field of gas turbines, such as turbojet engines, it is necessary to compromise the design criteria in order to achieve full power combustion chamber performance and also to achieve acceptable idle performance. The compromise between these operational parameters necessary to achieve minimum smoke emission, effective thermal strength of the chamber walls and the temperature distribution during full power operation; and to achieve efficiency and flame stability during idle performance is in the selection of the air fraction injected into the primary combustion zone during the various operating modes. The primary air is admitted into the combustion chamber through swirl vane structures, known as swirlers, through orifices located in the upstream end of the combustion chamber, and through openings in the inner and outer walls of the combustion chamber.
It is well known to use combustion chambers having two modules, one module being optimized for idler performance while the other module is optimized for full power performance. However, these chambers have not totally obviated the problems of the prior art since, aside for their increased weight and bulk, they create regulation difficulties in operational modes between idle and full power.
It has been proposed to obviate these difficulties by making the combustion chambers with a "variably geometry" wherein the air flow supply is continuously matched to the operational mode by a movable diaphragm which controls the air flowing through the combustion chamber air intakes. Typical examples of these systems are set forth in French Pats. Nos. 2,491,139 and 2,491,140. These patents show such control diaphragms controlling either the air flowing through the radial swirler (No. 2,491,139) on the air flowing the axial swirler (No. 2,491,140) of an otherwise conventional fuel injection apparatus. However, these devices suffer from poor air guidance across the swirler intakes and also produces significant wakes in the air flow within the combustion chamber.
It is also known to utilize an intermediate bowl structure interposed between the upstream end of the combustion chamber and the fuel injector. As shown in U.S. Pat. No. 4,162,611, in these devices the intermediate bowl has a frusto-conical portion flaring outwardly in a downstream direction and defines a plurality of small diameter holes through which highly pressurized air enters the atomized fuel cone issuing from the fuel injector. Due to the thorough mixing of the fuel and air achieved by the intermediate bowl member, it completes the function of the fuel injector and makes possible the formation of a primary "mini-zone" during idle conditions.
The intermediate bowl members also have air intakes which may be controlled by a modulating diaphgram, which diaphragm may also control the intake of air through the external swirler. Thus, the air flow can be controlled to modulate the exhaust flow so as to match the richness of the air-fuel mixture at the air exit of the intermediate bowl of operational conditions of the combustion chamber.